We propose to define further the molecular basis for the biological activity of the human androgen receptor. To reach this goal, we plan to detect and characterize the mutations of the androgen receptor in newborns with ambiguous genitalia due to a partial form of AIS and azoospermic individuals whose abnormality is related to a mild form of AIS. We will also explore the possibility that prostatic carcinoma cells, which have become resistant to the specific effects of suppression of androgen action, have become so due to somatic cell androgen receptor gene mutations causing a form of androgen insensitivity. In this application we will attempt to answer the following questions: 1) Can we expedite the diagnosis of AIS in newborns with ambiguous genitalia by testing for mutations of the androgen receptor gene? As a means of ruling out silent mutations, normal genetic variants of the androgen receptor gene of normal subjects will be identified. 2) Does the identification of a point mutation in the androgen receptor gene result in an abnormal biological activity? 3) Do some subjects with azoospermia present a mild form of AIS related to a point mutation of their androgen receptor gene? If so, what is the frequency of this abnormality and does it result in abnormal biological function? 4) In those subjects shown to have an abnormality in biological function of the androgen receptor associated with a point mutation in the androgen receptor gene, does immunocytochemical analysis of the androgen receptor in cultured genital skin fibroblasts demonstrate an effect on cytoplasmic/nuclear localization? 5) In some subjects with prostatic carcinoma, does resistance to hormonal therapy result from somatic cell mutations in the androgen receptor gene within a subpopulation of poorly differentiated cells from primary or metastatic lesions? The overall goal of our proposal is to establish structure/function correlates of naturally occurring androgen receptor gene mutations as a means to better understand the mechanisms of androgen action and to elucidate the causes for clinical conditions affecting human male sexual differentiation, fertility and prostatic carcinoma.